History of UNIX
UNIX was originally developed at Bell Laboratories as a private research project by a small group of people. Read all about the history of its creation.
Typographical conventions
In what follows, we shall use the following typographical conventions:
· Characters written in bold typewriter font are commands to be typed into the computer as they stand.
· Characters written in italic typewriter font indicate non-specific file or directory names.
· Words inserted within square brackets [Ctrl] indicate keys to be pressed.
So, for example,
% ls anydirectory [Enter]
means "at the UNIX prompt %, type ls followed by the name of some directory, then press the key marked Enter"
Don't forget to press the [Enter] key: commands are not sent to the computer until this is done.
Note: UNIX is case-sensitve, so LS is not the same as ls. The same applies to filenames, so myfile.txt, MyFile.txt and MYFILE.TXT are three seperate files. Beware if copying files to a PC, since DOS and Windows do not make this distinction.
UNIX Introduction
This session concerns UNIX, which is a common operating system. By operating system, we mean the suite of programs which make the computer work. UNIX is used by the workstations and multi-user servers within the school.
On X terminals and the workstations, X Windows provide a graphical interface between the user and UNIX. However, knowledge of UNIX is required for operations which aren't covered by a graphical program, or for when there is no X windows system, for example, in a telnet session.
The UNIX operating system
The UNIX operating system is made up of three parts; the kernel, the shell and the programs.
The kernel
The kernel of UNIX is the hub of the operating system: it allocates time and memory to programs and handles the filestore and communications in response to system calls.
As an illustration of the way that the shell and the kernel work together, suppose a user types rm myfile (which has the effect of removing the file myfile). The shell searches the filestore for the file containing the program rm, and then requests the kernel, through system calls, to execute the program rm on myfile. When the process rm myfile has finished running, the shell then returns the UNIX prompt % to the user, indicating that it is waiting for further commands.
The shell
The shell acts as an interface between the user and the kernel. When a user logs in, the login program checks the username and password, and then starts another program called the shell. The shell is a command line interpreter (CLI). It interprets the commands the user types in and arranges for them to be carried out. The commands are themselves programs: when they terminate, the shell gives the user another prompt (% on our systems).
The adept user can customise his/her own shell, and users can use different shells on the same machine. Staff and students in the school have the tcsh shell by default.
The tcsh shell has certain features to help the user inputting commands.
Filename Completion - By typing part of the name of a command, filename or directory and pressing the [Tab] key, the tcsh shell will complete the rest of the name automatically. If the shell finds more than one name beginning with those letters you have typed, it will beep, prompting you to type a few more letters before pressing the tab key again.
History - The shell keeps a list of the commands you have typed in. If you need to repeat a command, use the cursor keys to scroll up and down the list or type history for a list of previous commands.
Files and processes
Everything in UNIX is either a file or a process.
A process is an executing program identified by a unique PID (process identifier).
A file is a collection of data. They are created by users using text editors, running compilers etc.
Examples of files:
· a document (report, essay etc.)
· the text of a program written in some high-level programming language
· instructions comprehensible directly to the machine and incomprehensible to a casual user, for example, a collection of binary digits (an executable or binary file);
· a directory, containing information about its contents, which may be a mixture of other directories (subdirectories) and ordinary files.
The Directory Structure
All the files are grouped together in the directory structure. The file-system is arranged in a hierarchical structure, like an inverted tree. The top of the hierarchy is traditionally called root.
In the diagram above, we see that the directory ee51ab contains the subdirectory unixstuff and a file proj.txt
Starting an Xterminal session
To start an Xterm session, click on the Xterminal icon at the bottom of your screen.
An Xterminal window will appear with a Unix prompt, waiting for you to start entering commands.
UNIX Tutorial One
1.1 Listing files and directories
ls (list)
When you first login, your current working directory is your home directory. Your home directory has the same name as your user-name, for example, ee91ab, and it is where your personal files and subdirectories are saved.
To find out what is in your home directory, type
% ls (short for list)
The ls command lists the contents of your current working directory.
There may be no files visible in your home directory, in which case, the UNIX prompt will be returned. Alternatively, there may already be some files inserted by the System Administrator when your account was created.
ls does not, in fact, cause all the files in your home directory to be listed, but only those ones whose name does not begin with a dot (.) Files beginning with a dot (.) are known as hidden files and usually contain important program configuration information. They are hidden because you should not change them unless you are very familiar with UNIX!!!
To list all files in your home directory including those whose names begin with a dot, type
% ls -a
ls is an example of a command which can take options: -a is an example of an option. The options change the behaviour of the command. There are online manual pages that tell you which options a particular command can take, and how each option modifies the behaviour of the command. (See later in this tutorial)
1.2 Making Directories
mkdir (make directory)
We will now make a subdirectory in your home directory to hold the files you will be creating and using in the course of this tutorial. To make a subdirectory called unixstuff in your current working directory type
% mkdir unixstuff
To see the directory you have just created, type
% ls
1.3 Changing to a different directory
cd (change directory)
The command cd directory means change the current working directory to 'directory'. The current working directory may be thought of as the directory you are in, i.e. your current position in the file-system tree.
To change to the directory you have just made, type
% cd unixstuff
Type ls to see the contents (which should be empty)
Exercise 1a
Make another directory inside the unixstuff directory called backups
1.4 The directories . and ..
Still in the unixstuff directory, type
% ls -a
As you can see, in the unixstuff directory (and in all other directories), there are two special directories called (.) and (..)
In UNIX, (.) means the current directory, so typing
% cd .
NOTE: there is a space between cd and the dot
means stay where you are (the unixstuff directory).
This may not seem very useful at first, but using (.) as the name of the current directory will save a lot of typing, as we shall see later in the tutorial.
(..) means the parent of the current directory, so typing
% cd ..
will take you one directory up the hierarchy (back to your home directory). Try it now.
Note: typing cd with no argument always returns you to your home directory. This is very useful if you are lost in the file system.
1.5 Pathnames
pwd (print working directory)
Pathnames enable you to work out where you are in relation to the whole file-system. For example, to find out the absolute pathname of your home-directory, type cd to get back to your home-directory and then type
% pwd
The full pathname will look something like this -
/a/fservb/fservb/fservb22/eebeng99/ee91ab
which means that ee91ab (your home directory) is in the directory eebeng99 (the group directory),which is located on the fservb file-server.
Note:
/a/fservb/fservb/fservb22/eebeng99/ee91ab
can be shortened to
/user/eebeng99/ee91ab
Exercise 1b
Use the commands ls, pwd and cd to explore the file system.
(Remember, if you get lost, type cd by itself to return to your home-directory)
1.6 More about home directories and pathnames
Understanding pathnames
First type cd to get back to your home-directory, then type
% ls unixstuff
to list the contents of your unixstuff directory.
Now type
% ls backups
You will get a message like this -
backups: No such file or directory
The reason is, backups is not in your current working directory. To use a command on a file (or directory) not in the current working directory (the directory you are currently in), you must either cd to the correct directory, or specify its full pathname. To list the contents of your backups directory, you must type
% ls unixstuff/backups
~ (your home directory)
Home directories can also be referred to by the tilde ~ character. It can be used to specify paths starting at your home directory. So typing
% ls ~/unixstuff
will list the contents of your unixstuff directory, no matter where you currently are in the file system.
What do you think
% ls ~
would list?
What do you think
% ls ~/..
would list?
Summary
ls
list files and directories
ls -a
list all files and directories
mkdir
make a directory
cd directory
change to named directory
cd
change to home-directory
cd ~
change to home-directory
cd ..
change to parent directory
pwd
display the path of the current directory
UNIX Tutorial Two
2.1 Copying Files
cp (copy)
cp file1 file2 is the command which makes a copy of file1 in the current working directory and calls it file2
What we are going to do now, is to take a file stored in an open access area of the file system, and use the cp command to copy it to your unixstuff directory.
First, cd to your unixstuff directory.
% cd ~/unixstuff
Then at the UNIX prompt, type,
% cp /vol/examples/tutorial/science.txt .
(Note: Don't forget the dot (.) at the end. Remember, in UNIX, the dot means the current directory.)
The above command means copy the file science.txt to the current directory, keeping the name the same.
(Note: The directory /vol/examples/tutorial/ is an area to which everyone in the department has read and copy access. If you are from outside the University, you can grab a copy of the file here. Use 'File/Save As..' from the menu bar to save it into your unixstuff directory.)
Exercise 2a
Create a backup of your science.txt file by copying it to a file called science.bak
2.2 Moving files
mv (move)
mv file1 file2 moves (or renames) file1 to file2
To move a file from one place to another, use the mv command. This has the effect of moving rather than copying the file, so you end up with only one file rather than two.
It can also be used to rename a file, by moving the file to the same directory, but giving it a different name.
We are now going to move the file science.bak to your backup directory.
First, change directories to your unixstuff directory (can you remember how?). Then, inside the unixstuff directory, type
% mv science.bak backups/.
Type ls and ls backups to see if it has worked.
2.3 Removing files and directories
rm (remove), rmdir (remove directory)
To delete (remove) a file, use the rm command. As an example, we are going to create a copy of the science.txt file then delete it.
Inside your unixstuff directory, type
% cp science.txt tempfile.txt% ls (to check if it has created the file)% rm tempfile.txt % ls (to check if it has deleted the file)
You can use the rmdir command to remove a directory (make sure it is empty first). Try to remove the backups directory. You will not be able to since UNIX will not let you remove a non-empty directory.
Exercise 2b
Create a directory called tempstuff using mkdir , then remove it using the rmdir command.
2.4 Displaying the contents of a file on the screen
clear (clear screen)
Before you start the next section, you may like to clear the terminal window of the previous commands so the output of the following commands can be clearly understood.
At the prompt, type
% clear
This will clear all text and leave you with the % prompt at the top of the window.
cat (concatenate)
The command cat can be used to display the contents of a file on the screen. Type:
% cat science.txt
As you can see, the file is longer than than the size of the window, so it scrolls past making it unreadable.
less
The command less writes the contents of a file onto the screen a page at a time. Type
% less science.txt
Press the [space-bar] if you want to see another page, type [q] if you want to quit reading. As you can see, less is used in preference to cat for long files.
head
The head command writes the first ten lines of a file to the screen.
First clear the screen then type
% head science.txt
Then type
% head -5 science.txt
What difference did the -5 do to the head command?
tail
The tail command writes the last ten lines of a file to the screen.
Clear the screen and type
% tail science.txt
How can you view the last 15 lines of the file?
2.5 Searching the contents of a file
Simple searching using less
Using less, you can search though a text file for a keyword (pattern). For example, to search through science.txt for the word 'science', type
% less science.txt
then, still in less (i.e. don't press [q] to quit), type a forward slash [/] followed by the word to search
/science
As you can see, less finds and highlights the keyword. Type [n] to search for the next occurrence of the word.
grep (don't ask why it is called grep)
grep is one of many standard UNIX utilities. It searches files for specified words or patterns. First clear the screen, then type
% grep science science.txt
As you can see, grep has printed out each line containg the word science.
Or has it????
Try typing
% grep Science science.txt
The grep command is case sensitive; it distinguishes between Science and science.
To ignore upper/lower case distinctions, use the -i option, i.e. type
% grep -i science science.txt
To search for a phrase or pattern, you must enclose it in single quotes (the apostrophe symbol). For example to search for spinning top, type
% grep -i 'spinning top' science.txt
Some of the other options of grep are:
-v display those lines that do NOT match -n precede each maching line with the line number -c print only the total count of matched lines
Try some of them and see the different results. Don't forget, you can use more than one option at a time, for example, the number of lines without the words science or Science is
% grep -ivc science science.txt
wc (word count)
A handy little utility is the wc command, short for word count. To do a word count on science.txt, type
% wc -w science.txt
To find out how many lines the file has, type
% wc -l science.txt
Summary
cp file1 file2
copy file1 and call it file2
mv file1 file2
move or rename file1 to file2
rm file
remove a file
rmdir directory
remove a directory
cat file
display a file
more file
display a file a page at a time
head file
display the first few lines of a file
tail file
display the last few lines of a file
grep 'keyword' file
search a file for keywords
wc file
count number of lines/words/characters in file
UNIX Tutorial Three
3.1 Redirection
Most processes initiated by UNIX commands write to the standard output (that is, they write to the terminal screen), and many take their input from the standard input (that is, they read it from the keyboard). There is also the standard error, where processes write their error messages, by default, to the terminal screen.
We have already seen one use of the cat command to write the contents of a file to the screen.
Now type cat without specifing a file to read
% cat
Then type a few words on the keyboard and press the [Return] key.
Finally hold the [Ctrl] key down and press [d] (written as ^D for short) to end the input.
What has happened?
If you run the cat command without specifing a file to read, it reads the standard input (the keyboard), and on receiving the'end of file' (^D), copies it to the standard output (the screen).
In UNIX, we can redirect both the input and the output of commands.
3.2 Redirecting the Output
We use the > symbol to redirect the output of a command. For example, to create a file called list1 containing a list of fruit, type
% cat > list1
Then type in the names of some fruit. Press [Return] after each one.
pearbananaapple^D (Control D to stop)
What happens is the cat command reads the standard input (the keyboard) and the > redirects the output, which normally goes to the screen, into a file called list1
To read the contents of the file, type
% cat list1
Exercise 3a
Using the above method, create another file called list2 containing the following fruit: orange, plum, mango, grapefruit. Read the contents of list2
The form >> appends standard output to a file. So to add more items to the file list1, type
% cat >> list1
Then type in the names of more fruit
peachgrapeorange^D (Control D to stop)
To read the contents of the file, type
% cat list1
You should now have two files. One contains six fruit, the other contains four fruit. We will now use the cat command to join (concatenate) list1 and list2 into a new file called biglist. Type
% cat list1 list2 > biglist
What this is doing is reading the contents of list1 and list2 in turn, then outputing the text to the file biglist
To read the contents of the new file, type
% cat biglist
3.3 Redirecting the Input
We use the < symbol to redirect the input of a command.
The command sort alphabetically or numerically sorts a list. Type
% sort
Then type in the names of some vegetables. Press [Return] after each one.
carrotbeetrootartichoke^D (control d to stop)
The output will be
artichokebeetroot carrot
Using < you can redirect the input to come from a file rather than the keyboard. For example, to sort the list of fruit, type
% sort < biglist
and the sorted list will be output to the screen.
To output the sorted list to a file, type,
% sort <> slist
Use cat to read the contents of the file slist
3.4 Pipes
To see who is on the system with you, type
% who
One method to get a sorted list of names is to type,
% who > names.txt% sort < names.txt
This is a bit slow and you have to remember to remove the temporary file called names when you have finished. What you really want to do is connect the output of the who command directly to the input of the sort command. This is exactly what pipes do. The symbol for a pipe is the vertical bar
For example, typing
% who sort
will give the same result as above, but quicker and cleaner.
To find out how many users are logged on, type
% who wc -l
Exercise 3b
a2ps -Phockney textfile is the command to print a postscript file to the printer hockney.
Using pipes, print all lines of list1 and list2 containing the letter 'p', sort the result, and print to the printer hockney.
Answer available here
Summary
command > file
redirect standard output to a file
command >> file
append standard output to a file
command < file
redirect standard input from a file
command1 command2
pipe the output of command1 to the input of command2
cat file1 file2 > file0
concatenate file1 and file2 to file0
sort
sort data
who
list users currently logged in
a2ps -Pprinter textfile
print text file to named printer
lpr -Pprinter psfile
print postscript file to named printer
UNIX Tutorial Four
4.1 Wildcards
The characters * and ?
The character * is called a wildcard, and will match against none or more character(s) in a file (or directory) name. For example, in your unixstuff directory, type
% ls list*
This will list all files in the current directory starting with list....
Try typing
% ls *list
This will list all files in the current directory ending with ....list
The character ? will match exactly one character.So ls ?ouse will match files like house and mouse, but not grouse. Try typing
% ls ?list
4.2 Filename conventions
We should note here that a directory is merely a special type of file. So the rules and conventions for naming files apply also to directories.
In naming files, characters with special meanings such as / * & % , should be avoided. Also, avoid using spaces within names. The safest way to name a file is to use only alphanumeric characters, that is, letters and numbers, together with _ (underscore) and . (dot).
File names conventionally start with a lower-case letter, and may end with a dot followed by a group of letters indicating the contents of the file. For example, all files consisting of C code may be named with the ending .c, for example, prog1.c . Then in order to list all files containing C code in your home directory, you need only type ls *.c in that directory.
Beware: some applications give the same name to all the output files they generate. For example, some compilers, unless given the appropriate option, produce compiled files named a.out. Should you forget to use that option, you are advised to rename the compiled file immediately, otherwise the next such file will overwrite it and it will be lost.
UNIX was originally developed at Bell Laboratories as a private research project by a small group of people. Read all about the history of its creation.
Typographical conventions
In what follows, we shall use the following typographical conventions:
· Characters written in bold typewriter font are commands to be typed into the computer as they stand.
· Characters written in italic typewriter font indicate non-specific file or directory names.
· Words inserted within square brackets [Ctrl] indicate keys to be pressed.
So, for example,
% ls anydirectory [Enter]
means "at the UNIX prompt %, type ls followed by the name of some directory, then press the key marked Enter"
Don't forget to press the [Enter] key: commands are not sent to the computer until this is done.
Note: UNIX is case-sensitve, so LS is not the same as ls. The same applies to filenames, so myfile.txt, MyFile.txt and MYFILE.TXT are three seperate files. Beware if copying files to a PC, since DOS and Windows do not make this distinction.
UNIX Introduction
This session concerns UNIX, which is a common operating system. By operating system, we mean the suite of programs which make the computer work. UNIX is used by the workstations and multi-user servers within the school.
On X terminals and the workstations, X Windows provide a graphical interface between the user and UNIX. However, knowledge of UNIX is required for operations which aren't covered by a graphical program, or for when there is no X windows system, for example, in a telnet session.
The UNIX operating system
The UNIX operating system is made up of three parts; the kernel, the shell and the programs.
The kernel
The kernel of UNIX is the hub of the operating system: it allocates time and memory to programs and handles the filestore and communications in response to system calls.
As an illustration of the way that the shell and the kernel work together, suppose a user types rm myfile (which has the effect of removing the file myfile). The shell searches the filestore for the file containing the program rm, and then requests the kernel, through system calls, to execute the program rm on myfile. When the process rm myfile has finished running, the shell then returns the UNIX prompt % to the user, indicating that it is waiting for further commands.
The shell
The shell acts as an interface between the user and the kernel. When a user logs in, the login program checks the username and password, and then starts another program called the shell. The shell is a command line interpreter (CLI). It interprets the commands the user types in and arranges for them to be carried out. The commands are themselves programs: when they terminate, the shell gives the user another prompt (% on our systems).
The adept user can customise his/her own shell, and users can use different shells on the same machine. Staff and students in the school have the tcsh shell by default.
The tcsh shell has certain features to help the user inputting commands.
Filename Completion - By typing part of the name of a command, filename or directory and pressing the [Tab] key, the tcsh shell will complete the rest of the name automatically. If the shell finds more than one name beginning with those letters you have typed, it will beep, prompting you to type a few more letters before pressing the tab key again.
History - The shell keeps a list of the commands you have typed in. If you need to repeat a command, use the cursor keys to scroll up and down the list or type history for a list of previous commands.
Files and processes
Everything in UNIX is either a file or a process.
A process is an executing program identified by a unique PID (process identifier).
A file is a collection of data. They are created by users using text editors, running compilers etc.
Examples of files:
· a document (report, essay etc.)
· the text of a program written in some high-level programming language
· instructions comprehensible directly to the machine and incomprehensible to a casual user, for example, a collection of binary digits (an executable or binary file);
· a directory, containing information about its contents, which may be a mixture of other directories (subdirectories) and ordinary files.
The Directory Structure
All the files are grouped together in the directory structure. The file-system is arranged in a hierarchical structure, like an inverted tree. The top of the hierarchy is traditionally called root.
In the diagram above, we see that the directory ee51ab contains the subdirectory unixstuff and a file proj.txt
Starting an Xterminal session
To start an Xterm session, click on the Xterminal icon at the bottom of your screen.
An Xterminal window will appear with a Unix prompt, waiting for you to start entering commands.
UNIX Tutorial One
1.1 Listing files and directories
ls (list)
When you first login, your current working directory is your home directory. Your home directory has the same name as your user-name, for example, ee91ab, and it is where your personal files and subdirectories are saved.
To find out what is in your home directory, type
% ls (short for list)
The ls command lists the contents of your current working directory.
There may be no files visible in your home directory, in which case, the UNIX prompt will be returned. Alternatively, there may already be some files inserted by the System Administrator when your account was created.
ls does not, in fact, cause all the files in your home directory to be listed, but only those ones whose name does not begin with a dot (.) Files beginning with a dot (.) are known as hidden files and usually contain important program configuration information. They are hidden because you should not change them unless you are very familiar with UNIX!!!
To list all files in your home directory including those whose names begin with a dot, type
% ls -a
ls is an example of a command which can take options: -a is an example of an option. The options change the behaviour of the command. There are online manual pages that tell you which options a particular command can take, and how each option modifies the behaviour of the command. (See later in this tutorial)
1.2 Making Directories
mkdir (make directory)
We will now make a subdirectory in your home directory to hold the files you will be creating and using in the course of this tutorial. To make a subdirectory called unixstuff in your current working directory type
% mkdir unixstuff
To see the directory you have just created, type
% ls
1.3 Changing to a different directory
cd (change directory)
The command cd directory means change the current working directory to 'directory'. The current working directory may be thought of as the directory you are in, i.e. your current position in the file-system tree.
To change to the directory you have just made, type
% cd unixstuff
Type ls to see the contents (which should be empty)
Exercise 1a
Make another directory inside the unixstuff directory called backups
1.4 The directories . and ..
Still in the unixstuff directory, type
% ls -a
As you can see, in the unixstuff directory (and in all other directories), there are two special directories called (.) and (..)
In UNIX, (.) means the current directory, so typing
% cd .
NOTE: there is a space between cd and the dot
means stay where you are (the unixstuff directory).
This may not seem very useful at first, but using (.) as the name of the current directory will save a lot of typing, as we shall see later in the tutorial.
(..) means the parent of the current directory, so typing
% cd ..
will take you one directory up the hierarchy (back to your home directory). Try it now.
Note: typing cd with no argument always returns you to your home directory. This is very useful if you are lost in the file system.
1.5 Pathnames
pwd (print working directory)
Pathnames enable you to work out where you are in relation to the whole file-system. For example, to find out the absolute pathname of your home-directory, type cd to get back to your home-directory and then type
% pwd
The full pathname will look something like this -
/a/fservb/fservb/fservb22/eebeng99/ee91ab
which means that ee91ab (your home directory) is in the directory eebeng99 (the group directory),which is located on the fservb file-server.
Note:
/a/fservb/fservb/fservb22/eebeng99/ee91ab
can be shortened to
/user/eebeng99/ee91ab
Exercise 1b
Use the commands ls, pwd and cd to explore the file system.
(Remember, if you get lost, type cd by itself to return to your home-directory)
1.6 More about home directories and pathnames
Understanding pathnames
First type cd to get back to your home-directory, then type
% ls unixstuff
to list the contents of your unixstuff directory.
Now type
% ls backups
You will get a message like this -
backups: No such file or directory
The reason is, backups is not in your current working directory. To use a command on a file (or directory) not in the current working directory (the directory you are currently in), you must either cd to the correct directory, or specify its full pathname. To list the contents of your backups directory, you must type
% ls unixstuff/backups
~ (your home directory)
Home directories can also be referred to by the tilde ~ character. It can be used to specify paths starting at your home directory. So typing
% ls ~/unixstuff
will list the contents of your unixstuff directory, no matter where you currently are in the file system.
What do you think
% ls ~
would list?
What do you think
% ls ~/..
would list?
Summary
ls
list files and directories
ls -a
list all files and directories
mkdir
make a directory
cd directory
change to named directory
cd
change to home-directory
cd ~
change to home-directory
cd ..
change to parent directory
pwd
display the path of the current directory
UNIX Tutorial Two
2.1 Copying Files
cp (copy)
cp file1 file2 is the command which makes a copy of file1 in the current working directory and calls it file2
What we are going to do now, is to take a file stored in an open access area of the file system, and use the cp command to copy it to your unixstuff directory.
First, cd to your unixstuff directory.
% cd ~/unixstuff
Then at the UNIX prompt, type,
% cp /vol/examples/tutorial/science.txt .
(Note: Don't forget the dot (.) at the end. Remember, in UNIX, the dot means the current directory.)
The above command means copy the file science.txt to the current directory, keeping the name the same.
(Note: The directory /vol/examples/tutorial/ is an area to which everyone in the department has read and copy access. If you are from outside the University, you can grab a copy of the file here. Use 'File/Save As..' from the menu bar to save it into your unixstuff directory.)
Exercise 2a
Create a backup of your science.txt file by copying it to a file called science.bak
2.2 Moving files
mv (move)
mv file1 file2 moves (or renames) file1 to file2
To move a file from one place to another, use the mv command. This has the effect of moving rather than copying the file, so you end up with only one file rather than two.
It can also be used to rename a file, by moving the file to the same directory, but giving it a different name.
We are now going to move the file science.bak to your backup directory.
First, change directories to your unixstuff directory (can you remember how?). Then, inside the unixstuff directory, type
% mv science.bak backups/.
Type ls and ls backups to see if it has worked.
2.3 Removing files and directories
rm (remove), rmdir (remove directory)
To delete (remove) a file, use the rm command. As an example, we are going to create a copy of the science.txt file then delete it.
Inside your unixstuff directory, type
% cp science.txt tempfile.txt% ls (to check if it has created the file)% rm tempfile.txt % ls (to check if it has deleted the file)
You can use the rmdir command to remove a directory (make sure it is empty first). Try to remove the backups directory. You will not be able to since UNIX will not let you remove a non-empty directory.
Exercise 2b
Create a directory called tempstuff using mkdir , then remove it using the rmdir command.
2.4 Displaying the contents of a file on the screen
clear (clear screen)
Before you start the next section, you may like to clear the terminal window of the previous commands so the output of the following commands can be clearly understood.
At the prompt, type
% clear
This will clear all text and leave you with the % prompt at the top of the window.
cat (concatenate)
The command cat can be used to display the contents of a file on the screen. Type:
% cat science.txt
As you can see, the file is longer than than the size of the window, so it scrolls past making it unreadable.
less
The command less writes the contents of a file onto the screen a page at a time. Type
% less science.txt
Press the [space-bar] if you want to see another page, type [q] if you want to quit reading. As you can see, less is used in preference to cat for long files.
head
The head command writes the first ten lines of a file to the screen.
First clear the screen then type
% head science.txt
Then type
% head -5 science.txt
What difference did the -5 do to the head command?
tail
The tail command writes the last ten lines of a file to the screen.
Clear the screen and type
% tail science.txt
How can you view the last 15 lines of the file?
2.5 Searching the contents of a file
Simple searching using less
Using less, you can search though a text file for a keyword (pattern). For example, to search through science.txt for the word 'science', type
% less science.txt
then, still in less (i.e. don't press [q] to quit), type a forward slash [/] followed by the word to search
/science
As you can see, less finds and highlights the keyword. Type [n] to search for the next occurrence of the word.
grep (don't ask why it is called grep)
grep is one of many standard UNIX utilities. It searches files for specified words or patterns. First clear the screen, then type
% grep science science.txt
As you can see, grep has printed out each line containg the word science.
Or has it????
Try typing
% grep Science science.txt
The grep command is case sensitive; it distinguishes between Science and science.
To ignore upper/lower case distinctions, use the -i option, i.e. type
% grep -i science science.txt
To search for a phrase or pattern, you must enclose it in single quotes (the apostrophe symbol). For example to search for spinning top, type
% grep -i 'spinning top' science.txt
Some of the other options of grep are:
-v display those lines that do NOT match -n precede each maching line with the line number -c print only the total count of matched lines
Try some of them and see the different results. Don't forget, you can use more than one option at a time, for example, the number of lines without the words science or Science is
% grep -ivc science science.txt
wc (word count)
A handy little utility is the wc command, short for word count. To do a word count on science.txt, type
% wc -w science.txt
To find out how many lines the file has, type
% wc -l science.txt
Summary
cp file1 file2
copy file1 and call it file2
mv file1 file2
move or rename file1 to file2
rm file
remove a file
rmdir directory
remove a directory
cat file
display a file
more file
display a file a page at a time
head file
display the first few lines of a file
tail file
display the last few lines of a file
grep 'keyword' file
search a file for keywords
wc file
count number of lines/words/characters in file
UNIX Tutorial Three
3.1 Redirection
Most processes initiated by UNIX commands write to the standard output (that is, they write to the terminal screen), and many take their input from the standard input (that is, they read it from the keyboard). There is also the standard error, where processes write their error messages, by default, to the terminal screen.
We have already seen one use of the cat command to write the contents of a file to the screen.
Now type cat without specifing a file to read
% cat
Then type a few words on the keyboard and press the [Return] key.
Finally hold the [Ctrl] key down and press [d] (written as ^D for short) to end the input.
What has happened?
If you run the cat command without specifing a file to read, it reads the standard input (the keyboard), and on receiving the'end of file' (^D), copies it to the standard output (the screen).
In UNIX, we can redirect both the input and the output of commands.
3.2 Redirecting the Output
We use the > symbol to redirect the output of a command. For example, to create a file called list1 containing a list of fruit, type
% cat > list1
Then type in the names of some fruit. Press [Return] after each one.
pearbananaapple^D (Control D to stop)
What happens is the cat command reads the standard input (the keyboard) and the > redirects the output, which normally goes to the screen, into a file called list1
To read the contents of the file, type
% cat list1
Exercise 3a
Using the above method, create another file called list2 containing the following fruit: orange, plum, mango, grapefruit. Read the contents of list2
The form >> appends standard output to a file. So to add more items to the file list1, type
% cat >> list1
Then type in the names of more fruit
peachgrapeorange^D (Control D to stop)
To read the contents of the file, type
% cat list1
You should now have two files. One contains six fruit, the other contains four fruit. We will now use the cat command to join (concatenate) list1 and list2 into a new file called biglist. Type
% cat list1 list2 > biglist
What this is doing is reading the contents of list1 and list2 in turn, then outputing the text to the file biglist
To read the contents of the new file, type
% cat biglist
3.3 Redirecting the Input
We use the < symbol to redirect the input of a command.
The command sort alphabetically or numerically sorts a list. Type
% sort
Then type in the names of some vegetables. Press [Return] after each one.
carrotbeetrootartichoke^D (control d to stop)
The output will be
artichokebeetroot carrot
Using < you can redirect the input to come from a file rather than the keyboard. For example, to sort the list of fruit, type
% sort < biglist
and the sorted list will be output to the screen.
To output the sorted list to a file, type,
% sort <> slist
Use cat to read the contents of the file slist
3.4 Pipes
To see who is on the system with you, type
% who
One method to get a sorted list of names is to type,
% who > names.txt% sort < names.txt
This is a bit slow and you have to remember to remove the temporary file called names when you have finished. What you really want to do is connect the output of the who command directly to the input of the sort command. This is exactly what pipes do. The symbol for a pipe is the vertical bar
For example, typing
% who sort
will give the same result as above, but quicker and cleaner.
To find out how many users are logged on, type
% who wc -l
Exercise 3b
a2ps -Phockney textfile is the command to print a postscript file to the printer hockney.
Using pipes, print all lines of list1 and list2 containing the letter 'p', sort the result, and print to the printer hockney.
Answer available here
Summary
command > file
redirect standard output to a file
command >> file
append standard output to a file
command < file
redirect standard input from a file
command1 command2
pipe the output of command1 to the input of command2
cat file1 file2 > file0
concatenate file1 and file2 to file0
sort
sort data
who
list users currently logged in
a2ps -Pprinter textfile
print text file to named printer
lpr -Pprinter psfile
print postscript file to named printer
UNIX Tutorial Four
4.1 Wildcards
The characters * and ?
The character * is called a wildcard, and will match against none or more character(s) in a file (or directory) name. For example, in your unixstuff directory, type
% ls list*
This will list all files in the current directory starting with list....
Try typing
% ls *list
This will list all files in the current directory ending with ....list
The character ? will match exactly one character.So ls ?ouse will match files like house and mouse, but not grouse. Try typing
% ls ?list
4.2 Filename conventions
We should note here that a directory is merely a special type of file. So the rules and conventions for naming files apply also to directories.
In naming files, characters with special meanings such as / * & % , should be avoided. Also, avoid using spaces within names. The safest way to name a file is to use only alphanumeric characters, that is, letters and numbers, together with _ (underscore) and . (dot).
File names conventionally start with a lower-case letter, and may end with a dot followed by a group of letters indicating the contents of the file. For example, all files consisting of C code may be named with the ending .c, for example, prog1.c . Then in order to list all files containing C code in your home directory, you need only type ls *.c in that directory.
Beware: some applications give the same name to all the output files they generate. For example, some compilers, unless given the appropriate option, produce compiled files named a.out. Should you forget to use that option, you are advised to rename the compiled file immediately, otherwise the next such file will overwrite it and it will be lost.
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